Bile Acid Malabsorption



  • Bile acid malabsorption occurs when increased primary bile acids in the colon lead to chronic diarrhea and abdominal symptoms such as discomfort and bloating.
  • Definitions (1)
    • Type 1: Secondary to ileal dysfunction (e.g., Crohn disease, ileal resection, or radiation injury)
    • Type 2: Idiopathic
    • Type 3: Secondary to GI disorders other than ileal dysfunction (e.g., chronic pancreatitis, postcholecystectomy, celiac disease, bacterial overgrowth, and others)
    • Type 4: Increased bile acid synthesis induced by metformin (does not cause malabsorption but can cause similar symptoms to bile acid malabsorption due to effects of increased bile acid levels in colon)



  • Overall prevalence is estimated to be approximately 1% in Western countries (1).
  • Among patients with Crohn disease, with ileal resection, prevalence may be as high as 90% (1).
  • Among patients with functional diarrhea or diarrhea-predominant irritable bowel syndrome (IBS-D), ~30–40% shown to have dysregulation bile acid synthesis (1)
  • Bile acid malabsorption has been observed in up to 43% of patients with microscopic colitis, although data is conflicting and this was not replicated in other studies (1).
  • Prevalence of type 3 and type 4 bile acid malabsorption unknown (1)

Etiology and Pathophysiology

  • Primary bile acids are synthesized from cholesterol in the liver and secreted in bile after storage in the gallbladder, where they emulsify fats and play a role in micelle formation (1),(2),(3).
  • ~95% of bile acids are actively absorbed in the terminal ileum via the apical sodium bile acid transporter (2).
  • In the colon, secondary bile acids are formed by modification of primary bile acids by intestinal bacteria; these modifications increase passive absorption of secondary bile acids in the colon. Ultimately, a small amount of bile acids is passively reabsorbed in the colon (3).
  • After reabsorption in the ileum or colon, primary and secondary bile acids return to the liver via the portal vein for reuse (2).
  • Bile acid malabsorption in the ileum leads to increased levels of bile acids in the colon. There, the bile acids cause diarrhea via multiple mechanisms: stimulation of water, electrolyte, and mucus secretion; stimulation of colonic motility; alterations to microbiome (1).

Genetic variants in proteins involved in enterohepatic circulation of bile acids may contribute to bile acid malabsorption in murine models

Risk Factors

  • Inflammatory bowel disease (IBD), primarily Crohn disease (ileal resection or ileal disease)
  • Radiation therapy associated ileitis (e.g., pelvic radiation therapy)
  • Cholecystectomy
  • Microscopic colitis

General Prevention

No specific measures for prevention

Commonly Associated Conditions

  • Crohn disease
  • Celiac disease
  • IBS-D
  • Functional diarrhea

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